US2458659A - Discharge device for voltage measurement - Google Patents

Description

Jan. 11, 1949. A. w. VINGERHOETS ETAL 2$453,659

DISCHARGE DEVICE FOR VOLTAGE MEASUREMENT I Filed April 27, 1946 EUWOORP Patented Jan. 11, 1949 DISCHARGE DEVICE FOR VOLTAGE MEASUREMENT Antonius Wilhelmus Vingcrhoets and Hendrik N ieuwdorp,

Eindhoven, by mesne assignments,

Netherlands, assignors,

to Hartford National Bank and Trust Company, Hartford, Conn., as

trustee Application April 27 1946, Serial No. 665,392

In the Netherlands October 3, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires October 3, 1962 The present invention relates to direct-current voltage indicating arrangements.

When a voltage must be indicated, one sometimes encounters the dimculty that the input terminals of the indicating device cannot be connected directly to the terminals between which prevails the voltage to be measured, since one of the two input terminals is connected to an inter mediate point which exhibits potential differences relative to the two terminals of the voltage to be measured.

This diiiiculty becomes manifest, for example, when one of the terminals of a voltmeter is connected to ground and it is intended to use this meter to measure a source of supply whose electrical centre is connected to ground. In the case of alternating voltage this object may be achieved by utilising a separating transformer, but in the case of direct current other means must be found.

As a matter of fact, in measuring direct voltage use is made of a direct-current amplifier, but in this case also the same difliculty is experienced, since the input circuit and the output circuit of The present invention relates to a device for such amplifiers have a common connecting termiindicating direct voltage, in which this difllculty has been solved. In this device the grid and the cathodeof an amplifying tube (high-vacuum dis charge tube having a control electrode) are connected to points between which prevails a potential difference dependent on the voltage to be indicated. The anode circuit of this amplifying tube comprises an element having transferred to it the variations in the voltage to be indicated.

Said element is connected to that terminal of the meter which is not connected to the intermediate point, in such manner that this element is thus also included in the external circuit connecting the two input terminals of the meter. The latter is therefore not in series with the said element in the anode circuit of the amplifying tube, but the anode circuit and the external circuit of the meter, possess a common element, at which variations in voltage occur which are equal or proportional to the variations in the voltage to be measured or controlled.

' In order that the invention may be more clearly understood and readily carried into efiect, it will 5 Claims. (Cl. 171-95) Figures 3 to Tshowing circuit diagrams of constructional examples of the device according to the invention.

Figure 1 shows a simple circuit-diagram comprising an impedance I traversed by direct current, so that the terminals A and B exhibit a potential difference V. An intermediate point 2- of the impedance is connected to ground and exhibits potential differences Va and Vb relative to terminals A and B. The problem consists in -measuring the voltage V with the aid of a voltmeter 3, of which one of the input terminals is grounded, so that this terminal nected to intermediate point 2. The grounded input terminal of the voltmeter cannot be connected directly to one of the terminals of the voltage to be measured, since in this case the part of the impedance between the terminal considered and intermediate point 2 would be short-circuited. Consequently, only one. of the voltages Va and Vb can be measured directly and for measuring the total voltage V, which is the algebraic sum of the voltages V. and Vb, the indication of the measuring instrument can only be utilised, if it is certain that the voltage Va is always equal to the voltage 'Vb or at least proportional thereto. That such is not always the case will appear from the examples explained hereinafter.

If, as is shown in Figure 2, there is placed between the voltmeter 3 and the terminals of the voltage to be measured a direct-current amplifier 4 comprising a high-vacuum discharge tube having a control electrode and associated circuit elements, it is not possible for one of the terminals of the measuring instrument 3 to be also connected to ground, since in such amplifiers one of the input terminals is connected directly to one of the output terminals, as is indicated by a dotted line, due to the cathode being included in both the grid circuit and the anode circuit.

It can be seen from Figure 3 how this difficulty may be solved by the invention. The incandescent cathode 5 of an amplifying tube 6 is here connected to the negative terminal B of the voltnected to the positive terminal A through a source is exectively con-' is equal to the voltage to be measured itself.

The anode circuit of the tube comprises a source of supply 9 and a resistance ID. The anode current varies as a function of the grid voltage so that the voltage drop in resistance III varies according to the anode current. Resistance III consequently constitutes an element of the anode circuit which has transferred to it the variations "in the voltage to be measured. Terminal ll of the voltmeter 3 is connected 'to ground, i. e. to intermediate point 2. Terminal I2, which is not connected to this point, is connected to one end of element Ill included in the anode circuit of the tube, in such manner that it is thus also included inthe external circuit connecting the two input terminals II and I2 of the voltmeter 3. This circuit extends from terminal II via the grounded connection to the intermediate point 2 and thence via the part of impedance I between the fixed point 2 and the negative terminal B and further via resistance III to terminal I2.

As a result applied to meter 3 is the sum of two voltages, viz. the voltage drop in resistance I0, which comprises the variations in the voltage V to be measured, and the voltage Vb. Consequently, the variations in the voltage Vb are once again supplied to the meter 3. Apparently the device does not therefore satisfy the requirement imposed. The error in the indication brought about by the direct action of the voltagebetween terminal B and the intermediate point 2 on meter 3 is, however, negligible, since the amplification of tube 6 is preferably so great that the variations in the voltage Vb which are supplied directly are negligible relatively to those derived from resistance In. With a hundredfold amplification, for example, there will be obtained in most cases a sufficient approximation of the ideal condition. In many cases a comparatively low amplification will be sufiicient.

Due to this amplification, the voltage which is set up at meter 3 and the voltage which must be supplied by the source 9 might in certain cases become too high for practical use. From Figure 4 it will be seen, how this drawback may be avoided in a simple manner.

In this figure I3, I! and I5 are the current conductors of three-wire mains for direct current, which are supplied by two series-connected generators I61]. and IE1), whose mutual connection is conected to ground. Conductor I5 is the middle conductor, I3 is the positive and I4 the negative conductor. The task consists inmeasuring the voltage between conductors I3 and I4 in a point far remote from the point of supply with the aid of a measuring instrument of which one of the two input terminals is grounded. It is then not suflicient to measure the voltage of but one of the conductors relatively to earth, since due to leakage and irregular load the voltages which the conducors I3 and I4 exhibit relative to ground are not always equal or proportionally varying, even if this were the case with the terminal voltages of the dynamos I5 and I6. If, now, the full variations in voltage, which may be, for example, 20% of the nominal value of the mains voltage, are set up at the grid of the amplifying tube and these variations after a hundredfold amplification are transferred to the measuring instrument, the latter is suitable for a voltage which must be at least twenty times as aasaeea great as the mains voltage. It is evident that this is in many cases objectionable, but the difficulty can be easily obviated by deriving the control voltage from potentiometers, i. e. from a g potentiometer it for the positive terminal, which connects conductor I3 to ground, and from a potentiometer 98 for the negative terminal, which connects conductor I4 to ground. As before, we have an intermediate point 2 which exhibits the potential differences Va and Vb relative to the terminals of the voltage to be measured and which is connected to one of the supply terminals of the voltmeter 3. The grid and the cathode of amplifying tube 6 are now not connected to conductors I3 and I4, but are connected to taps I9 and of the potentiometers, which are chosen such that their potential difierences relatively to the intermediate point 2 are in the same relation to the voltages Va. and Vb. The cir- 20 cult is otherwise identical with that of Figure 3.

Figure 5 shows another possibility of construction of the device according to the invention, in which the drawbackof too high a voltage at the measuring instrument is also avoided. In this construction, like in that of Figure 4, the ter minals of the voltage to be measured are connected to the intermediate point 2 through potentiometers. As before, the grid of amplifying tube 6 is connected to a tap I9 of the potentiometer for the positive terminal, but instead of being connected, like in Figure 4, to a point of the potentiometer for the negative terminal, the cathode is now connected via a resistance 2| to the intermediate point 2. The source 9 of anode supply is connected to a tap of the potentiometer for the negative terminal, the tap 22. Consequently, the part Tb of potentiometer I8 between intermediate point 2 and tap 22 is included in the anode circuit of the amplifying tube. 0 terminal I I of the measuring instrument 3 is connected to ground, i. e. to the intermediate point 2, and terminal I2 is connected to point 22. In this case part Tb of potentiometer I8 constitutes the common element of the anode and of the external circuit of the meter 3 to which the variations in the voltage to be measured are transferred. The variations in the voltage Va are derived from the part Ta of potentiometer I|, located between tap l9 and intermediate point 2, and trans- 0 ferred to grid I of tube 6. The variations in control voltage bring about variations in the anode current, which in turn bring about corresponding variations in the potential drop across resistance rs traversed by anode current. This voltage drop comprises, in addition, the variations in the voltage Vb. Both variations are thus added in this resistance and with a suitable choice of resistance 2I and of taps I9 and 22 the total variations in voltage across resistance Tb which act upon the measuring instrument are proportional to those of the total voltage V. This may be proved as follows. If resistance H has a value Tc, the anode current ie of amplifying tube 8 produces in this resistance a voltage drop iarc. The current i2. in potentiometer I'I produces across part Ta. a

voltage drop iamn. Consequently, the grid voltage of tube 6 is composed of a positive component iiLTG and a negative component icfc.

The anode current of tube 6 will now adjust itself in such manner that icJ'c becomes approximately equal to iaJ'a. The resistances may be easily chosen such that the resulting grid voltage is low relatively to the product infa- For simplicitys sake it is assumed that To is equal to TIL, then it becomes equal to ia- The current to pro- As before,

duces in resistance Tb a voltage drop i.rb=i.rt. This resistance is traversed, in addition, by a current ib supplied by the voltage Vb- Consequently, the voltage drop Db in resistance Th is b=ia.1'b+ib.rb

Let the resistance of potentiometer H be RB and that of potentiometer l3 be R1 then so that & i,,.r,, Lb-Rb b or, as

El ll b Rb 12.12

Consequently, for Uh we may substitute ii ""41 5 L ""12. mafia If we choose Ra=Rb=R1 then Since, as a rule, R will be very high relative to Tb, the term with the minus sign is negligible relatively to V, so that the variations in the voltage drop across resistance Tb, which are supplied to the measuring instrument 3, are indeed proportional to those of the voltage V to be measured between the conductors l3 and I4.

If the variations of Va are-transferred to resistance Tb to a percentage larger than that of the variations of Vb, it is nevertheless possible to obtain a correct indication by connecting terminal |2 of the measuring instrument to potentiometer l8 not in the same point as the negative terminal of the source of supply 9, but, as is shown by dotted lines in Figure 5, in another tap 23. The farther tap 23 is removed from the intermediate point 2, the greater becomes the influence exerted by the voltage Vb on the indication of the measuring instrument.

That in the device of Figure 5 only a definite percentage of the voltage variations are transferred to the measuring instrument may in several cases lead to extension of this device by a second amplifying tube. A very simple manner of providing the latter consists in placing this tube between the two potentiometers in series with the first amplifying tube. The anode of the second tube- 24, as it appears from Figure 6, is then connected to the intermediate point 2. Grid 25 of tube 24 is connected, via a bias battery 26, to a tap 21 of the potentiometer I8 for the negative terminal. The cathode of tube '24 and terminal H of voltmeter 3 are connected to one end of potentiometer la. The element of the anode circuit of the first amplifying tube 1, which is also included in the external circuit connecting the two input terminals of the voltmeter 3, is in this case not an ordinary resistance, but discharge tube 24. c

Figure 7 shows an example of a device according to the invention for controlling instead of measuring a voltage, so that this voltage either varies in a definite manner or remains constant. a control tube is provided, viz. a. high-vacuum discharge tube having a control electrode, which is connected in series with a load whose voltage must be modulated, and this in such manner that the potential of the cathode differs from that of the negative terminal of the load. For this circult the invention is of particular importance, since the difliculties described in the preamble cannot be avoided by a symmetrical arrangement of the auxiliary device and, in addition, the control tube itself is included in the circuit and takes up a considerable variable voltage, so that it is out of the question whether Va and Vb must remain equal or proportional.

In Figure 7 a source of. supply 3| supplies a load 32 through a triode 33. The input terminals of the auxiliary device for the control of the voltage at the load are in this case connected to grid 34 and to incandescent cathode 35 of triode 33.

Cathode 35 is connected to the negative terminal 36 of the source of supply, i. e. to a point which exhibits potential differences Va and Vb relative to terminals Aand B of the voltage to be controlled. Va is in this case the terminal voltage of the source of supply 3| and Vb the voltage drop across control triode 33. The intermediate point is here the negative terminal 36 of the source of supply 3|.

A potentiometer I1 is provided for the positive terminal A and a potentiometer |8 .for the negative terminal B of the voltage to be controlled. An amplifying tube 6 is connected 'to these potentiometers in a manner similar to that of Figure 4. That supply terminal of the auxiliary device which is not connected to the interv mediate point 36, i. e. grid 34, is connected to resistance i through a source of bias 3! insuch manner that this resistance is thus included, in the same manner as in Figure 4, in the external circuit connecting the two supply terminals of the auxiliary device.

The voltages DB and he. of which the algebraic sum constitutes the positive component of the 4 grid voltage of tube 6, are here of opposite signs and the positive component is consequently equal to the difiference of the absolute values of 0a and. ob.

The same circuit may be utilised if an electromotive force is also active at the anode side of I the control tube. The source of supply maybe constituted. for example, by two series-connected generators 3| and 39, the latter. of which is indi- I cated by dotted lines in Figure 7. In certain cases this circuit may be preferable to that comprising a control tube which is connected directly to the load. Thus, it may be desirable for cathode 35 to be grounded, while it causes difliculty to ground one of the terminals of the load or one of the terminals of the source of supply, for example because the other terminal cannot withstand the full voltage of the load or of the source 01 supplyrelative to ground. In this case triode 33 is placed between the two parts of the source of supply. The grounding of cathode 35 is illustrated by a dotted line in Fig. '7.

The circuit shown in Fig. 7 may serve to control or to maintain constant of a high voltage, for example the voltage of an X-ray tube or of a device for testing insulators. By utilising a source of supply 31 having a variable electromotive force, it is possible to vary the voltage V that prevails between the terminals A and B. The latter voltage is within wide limits proportional to the: voltage of source 31, independent of the voltage of the generator 3| or of the generators 3| and 39. If the source 31 supplies a constant voltage, the voltage V remains constant, even if the voltage of the source of supply varies. This is of imf? pcrtance, if the source of supply used is a com denser or a battery of condensers.

The circuit shown in Figures and 6 may also be used in connection with a control device as shown in Fig. '7.

The invention may alternatively be applied for controlling a voltage by means of other auxiliary devices, such as electromagnetically operating control devices, of which one of the terminals is connected by grounding or in another manner to a point which always exhibits a definite potential difference relatively to terminal A as well as terminal B. 7

What we claim is;

1. Apparatus for indicating the voltage established across the output of a direct-current source by means of a voltage indicator one of whose input terminals is connected to an intermediate point in said source, said apparatus comprising an electron discharge device having a cathode, a control grid and an anode, said cathode and said grid being connected to two points in said source between which exists a p tential difference proportional to the output voltage of said source, a resistance element, an anode voltage supply connected to said anode and through said resistance element to said cathode, and means connecting the other input terminal of the indicator to a point in said resistance element.

2. Apparatus for indicating the voltage established across the output leads of a direct-current source by means of a voltage indicator, one of whose input terminals is connected to an intermediate point in said source, said apparatus comprising an electron discharge tube having a cathode, a control grid and an anode, a bias voltage supply, said cathode being connected to the negative lead of said source, said grid being connected through said bias voltage supply to the positive lead of said source, a resistance, an anode voltage supply connected to said anode and through said resistance to said cathode, and means connecting the other input terminal of said indicator to the junction of said anode voltage supply and said resistance.

3. Apparatus for indicating the voltage established between the output leads of a direct-current source by means of a voltage indicator one of whose input terminals is connected to an intermediate point in said source, said apparatus comprising a first potentiometer having a tap and being connected between the negative output terminal of the source and the intermediate point, a second potentiometer having a tap and being connected between the positive terminal of the source and the intermediate point, an electron discharge device having a cathode, a control grid. and an anode, said cathode being connected to the tap of said first potentiometer and said grid being connected to the tap of said second potentiometer,

a a resistance, an anode voltage supply connected between said anode and through said resistance to said cathode, and means connecting the other input terminal of said indicator to the junction of said supply and said resistance.

i. Apparatus for indicating the voltage established between the output terminals of a directcurrent source by means of a voltage indicator one,

\ intermediate point, an electron discharge device having a cathode, a control grid and an anode, said grid being connected to the tap of said second potentiometer, a resistance connected between the intermediate point and said cathode, an anode voltage supply connected between said anode and the tap of said first potentiometer,

and means connecting the other input terminal of the voltage indicator to the tap of said first potentiometer.

5. Apparatus for indicating the voltage established between the output leads of a direct current source' by means of a voltage indicator one of whose input terminals is connected to an intermediate point in said source, said apparatus comprising a first potentiometer having a tap and being connected between the negative lead of the source and the intermediate point, a second potentiometer having a tap and bein connected between the positive lead of the source and the intermediate point, the said first and second potentiometers being of equal value, an electron discharge device having a cathode, a control grid and an anode, said grid being connected to the tap or said second potentiometer, a resistance connected between the intermediate point and said cathode, the value of said re-v sistance being equal to the resistance existing between the tap of said first potentiometer and the intermediate point, an anode voltage supply connected between said anode and the tap of said first potentiometer, and means connecting the other input terminal of the voltage indicator to the tap of said first potentiometer.

ANTONIUS WILHELMUS VINGERHOETS.

HENDRIK NIEUWDORP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 7 Name Date 2,360,523 Simmons Oct. 7, 1944 2,364,687 Banker Dec. 12,1944

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